Custodians:

Deadwood at the Pond

Fallen willow adds to wildlife habitat

Karen Yukich

What type of tree is the dead one left to rot in the pond?

There are two types of large willow growing next to Grenadier Pond. The dead willow is a weeping willow….The willow is a short lived tree…In nature, a tree at the edge of a pond can die may be toppled by a beaver or strong wind, it become a place where wildlife can find food and cover & where “spawning …basking …drinking …breeding …raising young” can take place.

Why was the willow tree cut down?

A decision was made to fell the unsafe willow tree into the pond and leave it whole. When a tree becomes a safety hazard it is cut down. Any sign that the structure of the tree is compromised would have been acted on immediately especially one so close to the pathway. Signs that would warrant cutting down the tree would include significant wind or beaver damage as would indications that the tree was rotting such as dying branches in the crown of an old tree.

Wildlife Benefits

Dead trees left in place at the edge of a pond where they fall serve a number of purposes for wildlife:

Fallen trees are used as sunning spots for turtles and resting places for frogs & water snakes. At Grenadier, the turtles are more likely to be observed sunning off-shore on the snags sticking out of the pond. No doubt they feel safer where humans and off-leash dogs & possible prey have less access to them.

The fallen willow is a ramp way or a “dock”/platform used by small animals to more easily access the pond or for larger animals of all sizes to drink & feed from.

The branches provide cover & privacy when needed by animals such as the mallard & wood ducks found in grenadier pond. Ducks will breed and protect their young among these branches. As well, ducks feed off the algae that has attached to the submerged branches.

Fish can use the shade provided by the fallen tree to get a break from the sun’s heat and the submerged branches are used by small or young fish for shelter from water predators like larger fish. Shoreline debris such as this willow becomes a place for shore feeding animals such as…to dine on fish.

Some types of frogs will attach their eggs to submerged branches.

Water insects such as dragonflies and damselflies deposit larvae in shoreline debris, such as fallen trees, and graze on algae that grow there. Insect-eating birds then have a sheltered spot from which to feed.

Black crowned night herons, found along the shoreline of Grenadier Pond can perch on the branches of a shoreline snag to feed on prey such as the minnows found schooling in the submerged branches below.

Why is that fallen Willow Tree not removed from Grenadier Pond?

The fallen willow is purposely left where it is, half submerged at the edge of the pond, where it contributes to making the pond one that it is ideal for wildlife, plants and the ecological health of the pond as whole.

Other ecological benefits of the Fallen Willow:

• The plant populations along the shoreline also benefit from fallen trees being left in place: the sediments carried by the currents in the water tend to gather around the branches; water currents are dispersed when passing through the branches allowing silt to settle and reducing erosion along the shoreline in that area. The decaying branches also add nutrients to the sediment which are beneficial to plants, contributing to the muck on the floor of the pond. The plants which get a foothold in such favourable sediments will themselves further reduce the eroding effect of currents along the shoreline of the pond & further enhance the cover and food already provided by the fallen tree as it decays.

• The Benefits of muck:
Decomposing wood adds to the muck at the bottom of grenadier pond. “Mucky bottoms support insects and other invertebrates (e.g. crayfish) that are fed on by fish and wildlife” “gravel and silt” which gathers in shoreline vegetation and debris “good for fish spawning, mayflies for burrows, frogs for laying eggs”

Other animals using the willow:

Among Grenadier pond’s inhabitants and visitors is a diverse array of animal species including frogs & turtles, fish and water fowl, resident and migrating birds, beavers & mink as well as insects and small organisms that are less easy to see. Some of the visitors are land animals who use the pond to drink, feed on water plants, or prey on small animals. Migrating birds have a sheltered alternative to the windier & more exposed shorelines of Lake Ontario. All these animals benefit from the fallen willow being left where it is.

The fact that so many animals exist in and around Grenadier pond is remarkable considering the pond is located in the middle of Canada’s largest mega city. Even more remarkable when you consider that Grenadier pond is itself a part of a system of storm water retention ponds that naturally filters the city’s contaminants in the water before it flows to near-by Lake Ontario. The southern end of the pond is just meters away from high traffic roads whose cars generate massive amounts of air pollution. The foot traffic around the pond of millions of visitors every year is another stress on the pond’s survival.

Grenadier Pond management over time

Past

Today it is clear that Grenadier Pond’s location within 400 acres of parkland, much of it naturalized, is helping sustain the pond as a wetland ecosystem that serves both the pond residents as well as the land based wildlife of High Park. But this advantage was less evident for much of last half of the 20th century when the human uses of the park & the prevailing urban aesthetics of parklands dominated the landscape. Open areas emphasized mowed turf grass. The edges of Grenadier Pond, embanked by concrete, large remnants of which are still visible, were largely kept clear of debris and planted with ornamental trees. This willow tree would definitely have been “cleaned up” rather than left in place. You would not have seen the abundance of reeds and other plants growing in the pond or on its shores. You may still have seen some of the waterfowl and geese but missing would be the diversity of animals & plants and permanent residents that are present today. This took a change in perspective on how to manage High Park.

Present

A 1995 study is reflected in the current approach to maintaining Grenadier Pond & High Park. The decision to leave the fallen willow to decay in the pond is one of many decisions now employed that is making the difference to the ponds ability to sustain plant & animal communities. Today human usage of park is still accommodated, but now the needs of animals and plants and the ecosystems of the park are also being considered. This approach reveals a greater understanding by the public that natural corridors are needed in the city for our own health as well as for the survival of indigenous & naturalized wild animals & plants and to contribute locally to the health of the planet as a whole.

Future

Every year the fallen willow decays until there is no sign that it was there except for the stump on the shore. When it was first felled, the willow was the only one of its size on the east side of the pond contributing to the establishment of a more natural shoreline that provides habitat for wildlife. Ideally, as time passes, other trees and woody debris will grow, mature and die in numerous locations along the eastern edge of Grenadier Pond. As well, more of the cement will need to be removed to allow a more natural shoreline profile to develop. Plants will naturally invade the shoreline given these conditions and an established shoreline corridor for wildlife will be in place. The Grenadier Pond of the future is even more beautiful and diverse and the fallen Willow tree is contributing to that future.

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